The use of intravascular catheters has become an effective method for treating many types of vascular disease. In general, an intravascular catheter is inserted into the vascular system of the patient and navigated through the vasculature to a desired target site. Using this method, virtually any target site in the patient's vascular system may be accessed, including the coronary, cerebral, and peripheral vasculature. Examples of therapeutic procedures utilizing intravascular catheters include percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA). Catheters can also be used in other body lumens or organs for treatment and diagnosis, including the fields of neurology, urology and gastroenterology.
Intravascular catheters and other common catheters are often used in conjunction with a guidewire. A guidewire may be advanced through the patient's vasculature until it has reached a target location. Once in place, a catheter may be threaded onto the guidewire and urged distally until the distal end of the catheter reaches a target location.
One type of common catheter is a guide catheter which can be utilized during coronary angioplasty procedures to aid in delivering a balloon catheter or other interventional medical device to a treatment site in a vessel or other lumen within the body. In one application, a routine coronary angioplasty procedure, a guiding catheter is introduced into a peripheral artery and advanced over a guidewire through the aorta until the distal end of the guide catheter is engaged within the appropriate coronary ostium. Next, a balloon dilatation catheter is introduced over the guidewire and through the guide catheter. In order to function efficiently, guide catheters generally have a relatively stiff main body portion and a relatively flexible distal portion, including a soft distal tip. The stiff main body portion gives the guide catheter sufficient pushability and torqueability to allow the guide catheter to be inserted percutaneously into a peripheral artery or other lumen and advanced adjacent a desired site. However, a distal portion of the guide catheter requires sufficient flexibility so it can track over a guidewire and be maneuvered through a tortuous path to the treatment site.
A second type of common catheter is an angiographic or diagnostic catheter which can be used in evaluating the progress of disease, such as coronary artery disease. Angiography procedures are used to view the patency of selected blood vessels. In carrying out this procedure, a diagnostic catheter is advanced over a guidewire through the vascular system of the patient until the distal end of the catheter is steered into the desired body lumen site. As with the guide catheter, variation in stiffness over the length of the catheter is desired to aid in achieving access to a desired site through the tortuous anatomy.
Another common type of catheter is a balloon dilatation catheter which is adapted for use with a guidewire and typically classified as over-the-wire (OTW) or single operator exchange (SOE) in design. An OTW catheter includes a guidewire lumen extending from the distal tip of the catheter to the proximal end of the catheter. SOE catheters were developed in response to difficulties encountered when exchanging OTW catheters. Accordingly, SOE catheters have a relatively short guidewire lumen relative to the length of the catheter. Therefore, the length of guidewire extending beyond the body of the patient need only be slightly longer than the guidewire lumen of the catheter.
When in use, intravascular or other catheters enter a patient's vasculature or other body lumen at a convenient location and then are urged to a target region. Once the distal portion of the catheter has entered the patient's vascular or other system, the physician may urge the distal tip forward by applying longitudinal forces to the proximal portion of the catheter.
Frequently the path taken by a catheter through the vascular or other system is tortuous, requiring the catheter to change direction frequently. In some cases, it may even be necessary for the catheter to double back on itself. In order for the catheter to conform to a patient's tortuous vascular system, it is desirable that intravascular catheters be flexible, particularly near the distal end.
Further, while advancing the catheter through the tortuous path of the patient's vasculature or other system, physicians often apply torsional forces to the proximal portion of the catheter to aid in steering the catheter. Torsional forces applied at the proximal end must translate to the distal end to aid in steering. It is, therefore, desirable that the proximal portion of an intravascular catheter have a relatively high level of torqueability to facilitate steering.
The need for this combination of performance features suggests that it would be desirable for a catheter shaft to have variable flexibility along the length of the catheter. More specifically, it would be desirable for a catheter to have increased flexibility near the distal end of the catheter shaft and greater stiffness near the proximal end.
One approach used to balance the need for pushability and torqueability while maintaining adequate flexibility has been to manufacture a catheter that has two or more discrete tubular portions over its length, each having different performance characteristics. For example, a relatively flexible distal section may be connected to a relatively rigid proximal section. When a catheter is formed from two or more discrete tubular members, it is often necessary to form a bond between the distal end of one tubular member and the proximal end of another tubular member. This method requires substantial manufacturing steps to assemble the various sections and makes it difficult to manufacture the entire shaft utilizing coextrusion technology. Further, the shaft design is limited by the predetermined flexibility characteristics of each section and can include relatively abrupt changes in flexibility at material changes. A need, therefore, exists for catheter shafts that can be easily manufactured, such as by coextrusion, and yet are capable of having a variable stiffness without assembling components of the shaft.